Question

Consoder the following code:

<h:commandButton value="do" action="#{testBacking.do}">
   <f:ajax execute="@all" render="@all" listener="#{testBacking.listener}"/>
</h:commandButton>

I want to have a custom tag (with value based on server logic), in the Ajax response XML, something like the following:

<isValidationFailed> true </isValidationFailed>

I can use this data to re-enable the button (which was disabled when Ajax begin, to avoid double clicks) if validation is failed.

How can I achieve this (preferably without using any JSF 3rd party libraries)?

EDIT:

The example code, more precisely, should be like this:

<h:commandButton id="myButton" value="do" action="#{testBacking.do}">
 <f:ajax execute="id1" render="id2 myButton" listener="#{testBacking.listener}"/>
</h:commandButton>

Answer 1

This is only possible with a custom PartialViewContext which you load into your JSF application using a PartialViewContextFactory. The custom PartialViewContext should in turn return a custom PartialResponseWriter on PartialViewContext#getResponseWriter(). In this custom PartialResponseWriter, you should be able to add extensions to the XML response by calling startExtension() and endExtension() in endDocument(). Something like:

@Override
public void endDocument() throws IOException {
    Map<String, String> attributes = new HashMap<String, String>();
    attributes.put("name1", "value1");
    attributes.put("name2", "value2");
    startExtension(attributes);
    write("lorem ipsum");
    endExtension();
    super.endDocument();
}

This will then end up in the XML response as

<extension name1="value1" name2="value2">lorem ipsum</extension>

This is available and traversable by data.responseXML in jsf.ajax.addOnEvent() function.

---

Here’s a full kickoff example how you could utilize it in your particular case:

MyPartialViewContextFactory which provides the custom partial view context:

public class MyPartialViewContextFactory extends PartialViewContextFactory {

    private PartialViewContextFactory wrapped;

    public MyPartialViewContextFactory(PartialViewContextFactory wrapped) {
        this.wrapped = wrapped;
    }

    @Override
    public PartialViewContext getPartialViewContext(FacesContext context) {
        return new MyPartialViewContext(wrapped.getPartialViewContext(context));
    }

}

MyPartialViewContext which provides the custom partial response writer:

public class MyPartialViewContext extends PartialViewContextWrapper {

    private PartialViewContext wrapped;
    private PartialResponseWriter writer;

    public MyPartialViewContext(PartialViewContext wrapped) {
        this.wrapped = wrapped;
        this.writer = new MyPartialResponseWriter(wrapped.getPartialResponseWriter());
    }

    @Override
    public PartialResponseWriter getPartialResponseWriter() {
        return writer;
    }

    @Override
    public void setPartialRequest(boolean isPartialRequest) {
        wrapped.setPartialRequest(isPartialRequest);
    }

    @Override
    public PartialViewContext getWrapped() {
        return wrapped;
    }

}

MyPartialResponseWriter which writes <extension id="myextension"> with the body as JSON):

public class MyPartialResponseWriter extends PartialResponseWriter {

    public MyPartialResponseWriter(ResponseWriter wrapped) {
        super(wrapped);
    }

    @Override
    public void endDocument() throws IOException {
        startExtension(Collections.singletonMap("id", "myextension"));
        write("{\"validationFailed\": " + FacesContext.getCurrentInstance().isValidationFailed() + "}"); // Consider a JSON serializer, like Google Gson.
        endExtension();
        super.endDocument();
    }

}

To get it to run, register the factory as follows in faces-config.xml:

<factory>
    <partial-view-context-factory>com.example.MyPartialViewContextFactory</partial-view-context-factory>
</factory>

Here’s how you can access, parse and use the <extension id="myextension"> in your jsf.ajax.addOnEvent():

jsf.ajax.addOnEvent(function(data) {
    if (data.status == "success") {
        var args = JSON.parse(data.responseXML.getElementById("myextension").firstChild.nodeValue);

        if (args.validationFailed) {
            // ...
        }
        else {
            // ...
        }
    }
});

---

However, your particular functional requirement can be achieved in a different, likely simpler, manner. Just let the ajax request update the button itself and let the button’s disabled attribute evaluate true when there’s means of a successful postback.

<h:commandButton id="myButton" value="do" action="#{testBacking.do}" 
    disabled="#{facesContext.postback and not facesContext.validationFailed}">
    <f:ajax execute="id1" render="@this id2" listener="#{testBacking.listener}"/>
</h:commandButton>